1. Field of the Invention
This invention relates generally to self-drilling fasteners, and more particularly to a self-drilling screw for use with wood panels, such as oriented strand board (OSB), which drills its own two-stage pilot hole to enable screw threads to engage a material with reduced torque and splitting of the material.
2. Description of the Related Art
Self-drilling fasteners typically are utilized to attach a first member to a second base member and include some type of drill tip and threads along the shank of the fastener. The drill tip drills through both members and provides a pilot hole for the threads in order to secure the fastener to the base material with less torque and splitting of the base material. The drill tip and threads typically are modified for use with different materials.
Examples of self-drilling fasteners are illustrated in U.S. Pat. Nos. 4,601,625 and 5,067,864 both of which are assigned to the assignee herein. Those fasteners provide self-drilling threaded inserts that are utilized for drilling into substantially soft base materials, such as drywall, and include drill tips having central spikes positioned between two peripheral spikes. The inserts also include some type of toggle portion which can deflect laterally upon insertion of a separate screw within the insert to enable attachment of an article thereto. The central spike of the drill tip serves as a locator to prevent the tip from moving during initial drilling while the peripheral spikes cut the paper surface of the drywall.
Although such a fastener is most effective when utilized with soft drywall, it cannot be utilized with harder materials such as wood. Various self-drilling fasteners have been developed for drilling into wood and relatively soft wood panels, such as plywood, as well as dense composition wood panels such as particle board. Particle board, however, is very heavy and both materials are relatively expensive which makes them undesirable in many construction applications.
Wood panels known as oriented strand board (OSB) or waferboard are increasingly being utilized in construction. OSB substantially is composed of wood chips, has a hardness between that of plywood and particle board, is substantially lighter than particle board and is strong enough for most construction applications. Additionally, the cost of OSB is significantly lower than plywood or particle board which contributes to its popularity.
Existing fasteners utilized for plywood and particle board do not perform well with OSB. Plywood fasteners have difficulty drilling into the denser OSB while particle board fasteners are too harsh for OSB and frequently cause splitting.
It therefore would be desirable to provide a self-drilling fastener particularly for use with a material of medium density, such as OSB or waferboard, which readily drills its own pilot hole and fastens itself to the OSB with reduced torque and splitting.